Conventionally, a vehicle seat lifter that raises and lowers a seat using gears is known. In such a vehicle seat lifter, gears that mesh with each other cause backlash and the gears rattle due to the backlash. The backlash is also caused by errors or the like when mechanical processing of the gears. The backlash can be suppressed by adjusting the pitch of the mating gears with high accuracy. However, it is difficult to always process the mating gears with high accuracy so that the backlash does not occur, and it incurs a high cost.
Japanese Unexamined Patent Publication No. 2008-265365 discloses a vehicle seat lifter which suppresses rattling of gears due to backlash and in which a subgear meshes with a pinion gear that meshes with a sector gear, and the subgear is biased toward one side in a circumferential direction by a torsion spring, whereby the teeth of the pinion gear are pinched between the teeth of the sector gear and the teeth of the subgear.
However, in the vehicle seat lifter of Japanese Unexamined Patent Publication No. 2008-265365, when a load is applied to the subgear in a direction (the other side in the circumferential direction) opposite to the biasing direction (one side in the circumferential direction) of the torsion spring, for example, gears rattle. Moreover, when the subgear is provided as in Japanese Unexamined Patent Publication No. 2008-265365, the number of components increases, which makes it difficult to assemble the components and increases the manufacturing cost.